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Comparative performance of six holstein-friesian X guzera grades in Brazil. 6. Breed additive and heterosis effects on components of feed conversion effiency in heifers

F.E. Madalena^I; J.A.J. Paiva^II; R.L. Teodoro^II

^IEPAMIG, Departamento de Zootecnia, Escola de Veterinária, UFMG, Caixa Postal 567, 30161 Belo Horizonte, MG, Brasil. Send correspondence to F.E.M.
^IIEMBRAPA/EPABA-DPA, Av. Adhemar de Barros, 967, Ondina, 40000 Salvador, BA, Brasil
^IIIEMBRAPA-CNP-GL, 36155 Coronel Pacheco, MG, Brasil

ABSTRACT

Holstein-Friesian (HF) minus Guzera breed additive differences (g) and heterosis effects (h) were estimated for components of food conversion efficiency in 180 yearling heifers of six crossbred groups (1/4 to ≥ 31/32HF), in six 112 d duration feeding trials. These were conducted in two treatments: A, based on chopped elephant grass fed in the rainy season; B, based on elephant grass silage in the dry season. Each treatment was replicated in three years (1979 to 1981), with five heifers per crossbred group per replicate. Average daily liveweight gains in treatments A and B were 533 and 314 g/d. In treatment A, g-estimates were positive for dry matter and crude protein intakes, both per animal and per unit liveweight, but were negative for daily gain and for daily gain adjusted for dry matter intake. HF direct gene effects were unfavourable for the feed/gain conversion ratio. Heterosis enhanced daily gain, feed intake per animal and feed conversion efficiency, but did not affect feed intake per unit liveweight. In treatment B, positive g and h estimates were found for crude protein intake per animal. For crude protein intake per unit liveweight, g was positive and h non-significant (P > 0.10) when adjusted for initial weight, but g was non-significant and h positive upon adjustment for initial age. For all other traits, similar results were obtained with age or weight adjustments. The additive-dominance model fitted the data for all traits in treatment A, but not for daily gain, crude protein intake per unit liveweight and

Keywords: Holstein-friesian x guzera; Heterosis effects.

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